1. Field of the Invention
The present invention relates to a gear transmission including high and low speed gear trains one of which is selected. Especially, the gear transmission is provided in an axle drive unit equipped on a utility vehicle under a cargo deck of the utility vehicle.
2. Related Art
As disclosed in JP 2003-194097 A, there is a well-known axle drive unit which includes a gear transmission serving as a sub transmission connected to an output side of a belt type stepless transmission serving as a main transmission, and includes an axle driven by the gear transmission.
However, since the speed change operation of the sub transmission is manual, an operator must take the trouble to stop the vehicle for the sub speed change operation. Even if a load applied on the traveling vehicle, i.e., a load applied on (or a resistance against) the output shaft during traveling of the vehicle (hereinafter, referred to as “traveling load”) changes, the operator cannot operate the sub transmission so as to make the activated speed gear train of the sub transmission correspond to the real traveling load during traveling of the vehicle.
Further, an operator may wrongly select one of speed stages of the sub transmission, so that, during traveling of the vehicle, the wrongly selected speed stage may be incongruous to the rotary speed of the axle or of a prime mover so as to reduce the transmission efficiency or the insufficiency of torque, thereby causing an engine failure or other problems.